High-power LEDs that emit white light have become a choice for general solid-state lighting applications. Such high-power white LEDs have gained in brightness and can have luminous efficacies of 100 lm/W to beyond 200 lm/W. The input power of a contemporary single high-power LED is can be around 0.5 W to more than 10 W.
Such high-power LEDs can generate considerable amounts of heat while being only about 1 mm2 in area and relatively thin, so the demands on the packaging can be challenging and expensive. Today, the cost for a bare high-power LED chip typically can be well under $1.00 (e.g., $0.10), yet the packaged LED may cost around $1.50-$3.00. This makes a high output (e.g., 3000+ lumens) solid-state lighting device relatively expensive and not a commercially feasible alternative for fluorescent light fixtures, for example, which are commonly used in office, industrial and other lighting applications. Further, the optics required to convert the high brightness point light sources into a substantially homogeneous, broad angle emission for space illumination where glare control is important, for example, in office lighting applications, is extremely challenging.
The amount of light generated by solid-state lighting devices can be controlled using pulse width modulation (PWM). In such a case either full or no power is supplied in form of pulses at high frequencies with variable pulse widths. The ratio of the pulse duration per pulse period, generally referred to as the duty cycle, determines the average amount of power per pulse period. In PWM control the amount of generated light depends on the duty cycle.
Drawbacks of PWM in SSL systems can include effects due to frequent switching of drive currents such as power losses in the control system and other components of the lighting device due to parasitic electromagnetic effects, audible noise and component fatigue due to mechanical stress from vibrations caused by electrostriction or other effects and/or electromagnetic interference (EMI) from electromagnetic radiation emitted from the system.
Therefore there is a need for a solution that overcomes at least one of the deficiencies in the art.
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